Geological framework of the Archean and Paleoproterozoic Tanami Region, Northern Territory |
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| Authors: | A J Crispe L C Vandenberg I R Scrimgeour |
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| Institution: | (1) Northern Territory Geological Survey, GPO Box 3000, Darwin, NT 0801, Australia |
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| Abstract: | The Tanami Region, a poorly exposed, mostly Paleoproterozoic province within the North Australian Craton, hosts a number of
significant gold deposits in diverse settings. Rare exposures of 2,520–2,500 Ma amphibolite facies Archean gneiss and metasedimentary
rocks form basement to the thick overlying metasedimentary succession of the 1,880–1,830 Ma Tanami Group. The basal unit of
the Tanami Group is the Dead Bullock Formation, a fining-upward deep-water succession dominated by siltstone, carbonaceous
siltstone, iron-rich siltstone and mafic sills. Carbonaceous- and iron-rich lithologies in the upper Dead Bullock Formation
represent important hosts for gold mineralization. The conformably overlying Killi Killi Formation represents turbiditic sedimentary
rocks that are correlated with the widespread Lander Rock beds of the Arunta Region. Sedimentation of the Tanami Group was
terminated by regional deformation and greenschist to amphibolite facies metamorphism during the Tanami Event (D1/M1), at around 1,830 Ma. The Tanami Group is unconformably overlain by rhyolite, siliciclastic sedimentary rocks, and felsic
ignimbrite of the Ware Group that were deposited at about 1,825–1,810 Ma. Subsequent ESE–WNW to SE–NW directed shortening
(D2), followed by NE–SW to E–W directed shortening (D3), has resulted in open NE F2- and NW F3-trending folds in both the Tanami and Ware Groups. Voluminous granitoids, dominated by I-type, biotite granodiorite, and
monzogranite were intruded in the interval 1,825–1,790 Ma and have been subdivided using geochemical criteria into the Birthday,
Frederick, and Grimwade Suites. Basalt and immature sedimentary rocks of the Mount Charles Formation are restricted in extent
to the Tanami mine corridor, and are interpreted to reflect a continental rift succession that was deposited around 1,800 Ma,
with an early Archean sedimentary provenance. Steep S to SE dipping F4-fold structures of Tanami and Ware Group metasedimentary rocks, many spatially associated with 1,825–1,790 Ma granitoid intrusions,
indicate a period of SSE-directed regional shortening (D4) syn-to-post the regional granitoid intrusive phase. A network of N to NW striking faults, several of which are interpreted
as oblique thrusts with a component of left lateral movement, indicates a period of D5 convergence during WSW–ENE to E–W directed shortening. The Tanami mine corridor fault system comprises a network of N, NE
to ENE striking D5 faults that merge with N to NW striking faults and probably accommodated movement between granite core domains. D5 faulting is associated with the main phase of gold mineralization in suitable structural–lithological traps. The Paleoproterozoic
basement of the Tanami Region is unconformably overlain by quartz sandstone, lithic arenite, and conglomerate of the Pargee
Sandstone. Pargee Sandstone may represent syn-tectonic sedimentation related to the 1,730 Ma Strangways Orogeny, and is unconformably
overlain by the late Paleoproterozoic platform cover succession of the Birrindudu Group. The Paleoproterozoic basement and
cover sequences have subsequently undergone several episodes of faulting, collectively termed D6+. The Paleoproterozoic evolution of the Tanami Region is interpreted to have occurred in an intracratonic setting, but was
fundamentally influenced by tectonic events in the adjacent Halls Creek Orogen (1,835–1,805 Ma Halls Creek Orogeny) and Arunta
Region (1,815–1,800 Ma Stafford Event). The boundaries between the Tanami Region and Kimberley Region to the northwest and
the Arunta Region to the southeast are transitional, and are largely defined by the presence or absence of identifiable Dead
Bullock Formation. |
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| Keywords: | Tanami Region North Australian Craton Paleoproterozoic Stratigraphy Structural geology |
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